All of these devices operate in the 500- to 650-MHz range,
which is a key part of the white-space territory. Interference is
expected. As a result, wireless mike users, who are licensed users
of that spectrum, can be protected. They will be entered into the
national database so they will be protected by a 1-km radius from
their location.
In addition, there’s a listen-before-you-transmit rule. All WSDs
must have a super-sensitive receiver (–94- to –116-dBm range)
that listens to the desired channel to see if other signals are present.
If so, the unit can’t transmit. Instead, it will jump to another
potential channel and repeat the listening process. The frequencyagile
WSD will eventually find a channel and transmit. WSDs
will, for the most part, be cognitive radios.
Furthermore, according to the official guidelines, fixed stations
on channels 2, 3, and 37 won’t be operable. Portable or mobile
WSDs are restricted to channels 21 through 51 except channel
37. (Channel 37 is a protected channel for radio astronomy and
for medical telemetry.) All potential devices will be tested by
the FCC and approved as either a fixed or master device or as a
portable client device.
In addition, basestations or fixed-master wireless nodes can’t
use more than 1 W of power or 4 W of effective isotropic radiated
power (EIRP). In other words, the transmitter power is no more
than 1 W, but the antenna gain makes up for it. A mobile WSD
is limited to 100 mW or 40 mW if it’s operating on a channel adjacent to a nearby TV station. Furthermore, all units must have
adaptive power control that can automatically adjust for minimum
power to maintain a link.
As indicated earlier, WSDs will operate under the FCC’s Part
15 unlicensed rules and regulations. No formal wireless radio
standards exist for WSDs, but several technologies are under
test. One is Wi-Fi. Why not use the 802.11 standard in the white
spaces? The same goes for 802.16 WiMAX.
The IEEE has joined the mix, too, with an effort designated
the 802.22 Wireless Regional Area Network working group. It’s
developing a physical layer (PHY) and media-access-controller
(MAC) layer standard for cognitive radios that can operate within
the white-space guidelines. Another IEEE activity involves the
P1900 standards group. A recent project dubbed P1900.4a will
look at new architectures and interfaces that can provide dynamic
spectrum access in the white-space bands.
WHAT TO DO WITH WHITE SPACE?
With approval in tow and great potential on tap, what new
services and products can we expect? First, there’s wireless localarea
networks (WLANs). Just like Wi-Fi, WLAN could be used in
the home, office, or public spaces. It also offers longer range and
greater reliability.
Wireless broadband could provide an alternative to 3G and 4G
cellular data services and WiMAX. A wireless Internet service
provider (WISP) may be able to offer services in rural areas or
sections of the country where there’s no broadband. Stimulus
money could help encourage its growth.
Then, there’s consumer entertainment or home monitoring and
control wireless. Industry, municipalities, and utilities could use
it for telemetry and remote control. Also, consider cordless telephones,
video surveillance, and wireless backhaul.
Many WSDs are under development, and they could start to
arrive in the coming years. Some manufacturers may be waiting
on a standard, but some are not. Is a single standard really necessary
with its implied interoperability?
No one knows for sure how this will unfold. Is it just a big boondoggle
where interference is rampant and spectrum is wasted? Or
will we really enjoy and benefit from some new and better wireless
products and services? We’ll find out soon enough.